A number of 4-(4-phenyl-1-piperazinyl)phenyl derivatives are known from U.S. Pat. Nos. 4,267,179 and 4,619,931 and from EP-A-0,228,125 as intermediates for the preparation of compounds having antifungal and antibacterial properties. Additionally, the compound N,N'-bis(4-hydroxyphenyl)piperazine is known from U.S. Pat. No. 3,720,690, as an intermediate for the preparation of a compound useful in the treatment of allergic and autoimmune diseases.